In a typical modern locomotive, a diesel engine is used to provide mechanical energy to a electric generator. The generator converts this mechanical energy into electrical power which is used to operate a plurality of direct current (dc) traction motors, each driving a separate drive axle having a pair of drive wheels connected thereto.
Wheel slip usually occurs during acceleration, and can take two forms. The first type, referred to as differential wheel slip, occurs when at least one set of drive wheels maintains tractive contact with the rail while at least one set of the remaining drive wheels slip. A second type of wheel slip is synchronous slip which occurs when none of the drive wheels maintains tractive contact with the rail and all of the drive wheels slip more or less simultaneously.
Wheel slip has long been a problem in locomotives and many systems have been developed which either reduce or completely eliminate wheel slip. A common scheme is to compare speed signals from driven and idler wheels or speed signals from each of several driven wheels or highest and lowest speed signals from traction motors. A slip condition is presumed to exist if the compared speed signals differ by more than a preselected magnitude. In the above mentioned systems, sensors, such as speed transducers, are used to produce the speed signals and such sensors add extra costs to wheel slip control systems.
An example of a wheel slip control system using speed sensors is disclosed in U.S. Pat. No. 4,463,289 issued July 31, 1984 to Young. In Young, the speeds of individual drive wheels are sensed and a differential signal is produced in response to a difference between the highest and lowest sensed wheel speeds. The differential signal is then compared to a creep reference signal to produce a slipping signal which is used to control generator output. The creep reference signal represents an amount of wheel slip at which maximum adhesion occurs. When a wheel begins to slip, the differential signal increases. This increases the slipping signal resulting in a reduction of the generator power.
The present invention is directed towards addressing the above mentioned problems by controlling differential wheel slip in a locomotive without requiring speed sensors. Other aspects, objects and advantages can be obtained from a study of the drawings, the disclosure, and the appended claims.